INTRODUCTIONDental caries is a disease that is characterized by the localized destruction of susceptible dental hard tissue by acidic by-products from bacterial fermentation of dietary carbohydrates. The process is a dynamic interaction at the biofilm-tooth interface characterised by alternating cycles of demineralisation and remineralization. A caries/carious lesion are a detectable change in the tooth structure that results from this interaction. The changes may range from initial outer surface demineralization, at the molecular level, through subsurface demineralization producing enamel white-spot lesion formation, through macroscopic lesion cavitation, to dentine and pulpal infection, to ABSTRACT Background: Pit and fissure caries presents diagnostic challenges due to its anatomical complexity and fluoride exposure. ICDAS II is a coding system for caries detection using clinical visual inspection. It identifies carious lesions by the change in colour, texture and surface integrity. Magnification might facilitate better detection of the lesions by enhancing the visual acuity. Thus, the objective of this study is to compare the reliability and validity of ICDAS II in detection of occlusal caries, with and without magnification, by using histological standard. Methods: This single blinded, randomized study included 334 unrestored extracted human premolars and molars. Two examiners independently scored pit and fissure caries status using ICDAS II criteria without magnification and later under 6 x magnification using surgical microscope. The samples were sectioned and lesions were scored using the ERK histological criteria, under Stereo microscope. The scores of the examiners were correlated with the histological scoring. Kappa statistics and Spearman correlation coefficients were performed. Optimal sensitivity, specificity of visual and enhanced visual examination was calculated by Receiver Operating Characteristic Curve (ROC). Likelihood ratios (LR) were also calculated. Results:The kappa values for Inter examiner reproducibility of visual and enhanced visual examination under microscope were 0.638-0.694 and for histological examination it was 0.979. Intra examiner reproducibility for visual and enhanced visual examination was 0.665 -0.594. There was a strong relationship between visual, enhanced visual and histological examinations. Spearman's correlation coefficient of ICDAS-II visual and enhanced visual examination for each examiner, to ERK histological scores was 0.869-0.848. The sensitivity and LR+ for visual and enhanced visual examination was decreased as the ICDAS score was increased and specificity and LR-increased with increased ICDAS score. Conclusions: Reliability and validity of ICDAS scoring in detecting occlusal caries under magnification did not differ from clinical visual inspection.